Receiver noise control circuits



sept. 16, 1941.

AVC

B. D. H. TELLEGEN ET AL RECEIVER NOISE CONTROL CIRCUITS Original Filed Oct. 28, 1935 ngi SOURCE FPL' fyi)

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TUA/0 BE7-NEEN 70o @No 900 A467595 R W 4 v NToR IN E 5 BERNARDUS D.H.TELLEGEN /g VAN C. HENRIQUEZ l m ATTORNEY.

@ l] l 70p Patented Sept. 16, 1941 @FMC RECEIVER NOESE CNTRL CBLCUITS Bernardus D. H. Tellecfen and Vivian Cohen aan Henrquez, Eindhoven,

by mesne assignments,

Netherlands, assignors,

to Radio Corporation of America, New York, N. Y., a corporation of Delaware Appli February 1, 1935 -18 Ciairns.

This invention relates to a circuit arrangement for eliminating disturbances in radio receiving sets and more particularly for suppressing disturbances resulting either from atmospheric conditions or originating from machines or apparatus. These disturbances are often reproduced as short explosions by the loudspeaker of the receiving set.

It has already been proposed to reduce the amplification of the high or intermediate frequency amplifier of the receiver for the duration of a disturbance either by raising the damping of the tuned high or intermediate frequency circuits during this time or by altering the grid voltage, in such a manner that the working point on the characteristic curve of an amplifying tube is shifted toward a point where the slope is smaller. However, these methods have the drawback that upon receiving a disturbance the carrier wave of the signal to be received is also suppressed, and this also manifests itself as a disturbance. In addition, due to the abrupt increase of the damping of an oscillatory circuit or due to the sudden decrease in amplification the oscillatory circuit or the following oscillatory circuits are made to oscilla-te in their natural frequency, which also causes an explosion-like disturbance which is reproduced by the apparatus.

According to the invention these defects are avoided by providing that upon receiving a disturbance the amplification of the low frequency amplifier of a receiving set is automatically reduced by a mechanical or electric switching arrangement controlled by the disturbance itself, the switching impulse resulting from the switching operation being compensated by an opposite switching impulse which is also controlled by the disturbance.

The mechanical or electric switching device may be controlled, for instance, by a rectier coupled with the high or intermediate frequency amplifier of the receiver. This rectifier is given such a threshold sensitiveness by means of a suitable bias that only disturbances whose arnplitude exceeds by a definite amount the arnplitude of the incoming carrier wave produce a current in the` rectifier, which current releases the electrical or mechanical switching arrangement.

It is also possible to control the mechanical or electrical switching device by a rectifier to be fed from an amplifier which is tuned to a wave different from the carrier wave to be received, for

cation Gctober 28, 1935, Serial No. 47,098. Renewed September 23, 1938.

in Germany (Ci. 25d-20) instance, to a wave above the range of wave lengths to be received. This is based on the realization that, as is well known, a disturbance comprises a very broad frequency spectrum so that its components lie not only inside but also outside the receiving range. Such an arrangement together with an additional amplifier need not have any or only a small threshold sensitiveness so that the disturbances are eliminated to a much larger degree.

The additional amplifier may also be aperiodic.

The invention will be more clearly understood by reference to the accompanying drawing representing, by way of example, a few embodiments thereof, wherein Fig. l shows one form of the invention; Fig. 2 shows still another modincation; and Fig. 3 illustrates another embodiment and Fig. 4 illustrates another modification.

In Fig. 1, D denotes an anode-rectifying tube to whose grid are supplied high or intermediate frequency alternating voltages through a tuned transformer T. The working point on the charcteristic curve of the tube may be adjusted in a suitable manner with the aid of a voltage source E51. The anode circuit of this tube D comprises the primary winding P1 of a low frequency transformer T1 Whose secondary Winding S1 isconnected to the grid of an amplifying tube V.

The anode voltage of the tube D is supplied from the voltage source Ea through a relay switch S which is normally closed. The exciting winding R of this relay is interposed in the anode cir-cuit of a rectifying tube G, for instance in anode-rectifier arrangement, whose grid circuit comprises a coil W which is coupled with the grid circuit of the tube D. By means of a voltage .source EQ2 the grid bias of the tube G is so adjusted that an anode current can flow only if a disturbance arrives whose amplitude exceeds double the value of that of the incoming carrier wave. Preferably, the latter amplitude is kept constant or substantially constant in the receiver by automatic volume control.

When the disturbance amplitude exceeds the threshold sensitiveness of the rectifier G the eX- citing winding of the relay S is traversed by a current by which the switch S is opened, and the anode current circuit of the tube D is interrupted. As soon as the disturbance amplitude has decreased below the threshold Sensitiveness of the rectiiier G, the switch S is closed again. During the time interval between opening and closing the switch the low frequency amplifying tube V receives no disturbing voltage so that the disturbance cannot manifest itself in the reproducing apparatus. At the same time the desired lowV frequency alternating currents are suppressed. If, however, the interruption does not exceed about 1/25 second or the disturbances do not succeed each other too rapidly, this is not brought out in an annoying manner. The abrupt current variation occurring on opening and closing the switch S causes a voltage impulse in the secondary winding S1 of the transformer T1 which Vimpulse is reproduced in the apparatus after having been amplified. Consequently, although an incoming disturbance cannot directly manifest itself, it indirectly produces again an undesirable disturbance due to the switching operation brought about by it.

In order to suppress this switching impulse in the circuit arrangement shown in Fig. 1, the grid circuit of the amplifying tube V comprises the secondary winding S2 of a transformer T2 whose primary winding P2 is connected through a resistance R1 and the switch S to the source of anode Voltage Ea. The windings of the transformers T1 and T2 are so connected and the resistance R1 has such a value that on opening and closing the switch S equal but opposite voltages are induced in the secondary windings so that the switching impulse cannot affect the grid of the tube V. Obviously it is required for a perfect operation of this arrangement that the compensating circuit Ea, S, P2, R1 exactly correspond to the circuit Ea, S, P1, D; so that the resistance R1 is preferably replaced by a tube having the same characteristic curve as the tube D. With these compensating arrangements, equalization of all earth and switching capacities concerned requires particular attention.

Fig. 2 represents another circuit arrangement according to the invention, but Without a mechanical relay, wherein upon receiving a disturbance the low frequency amplifier is made inoperative by shifting the grid bias of a low frequency amplifyingtube. In this arrangement the high or intermediate frequency oscillations, amplified f in a receiver E provided with automatic volume control, are supplied through a preferably tuned transformer T to an indirectly heated diode rectifier D. The low frequency alternating voltage,v set up after the rectification at the potentiometer P, is impressed through a condenser C1 on the grid of one of the push-pull connected amplifying tubes V1 and V2. The grids of these tubes are connected together through a resistance Rg1, and to the cathodes through a resistance R and a voltage source Egz for adjusting the grid bias.

The anode circuits of the tubes V1 and V2 comprise resistances R111 and Rs2 through which the anode direct Voltage is supplied. The primaryV winding l of the low frequency transformer T1, whose secondary winding (which is electrostatically shielded by means of `a screen S), lies in the grid circuit of another low frequency amplifying tube V3, is connected in Vparallel with said re- 1 sistances.

The low frequency oscillations supplied to the tube V1 are amplified and impressed on the following tube V3 whose anode circuit comprises,

for instance, av reproducing apparatus or is coupled with further amplifying stages. The input transformer'T of the rectifying tube D is coupled with a coil W, one end of which is connected to the anode of rectifier G and whose other end is connected to the cathode. Y The anode of diode G is connected to its cathode through the resistance R shunted by a condenser C4; by means of a voltage source E the anode receives such a negative bias across the resistance R that the rectifier G is currentless so long as no disturbances occur, and consequently an alternating voltage is induced on the coil W, which voltage is kept constant by the automatic volume control of the high or intermediate frequency .amplier preceding the rectifying tube D.

As soon, however, as a short disturbance occurs and produces in the coil W a Voltage having a larger amplitude than the said alternating voltage, a current producing a voltage drop at the resistance R flows in the rectifier G. This voltage drop increases the grid bias of the amplifying tube V1, to such an extent that this tube is blocked, so that the disturbance cannot reach the reproducing apparatus'.

In order that the switching operating, which causes blocking of the amplifier V1, does not work out itself in an annoying manner, the tube V2, connected in push-pull arrangement with the tube V1, is simultaneously blocked by means of the voltage drop at the resistance R. If both tubes are of the same type the abrupt anode voltage variations of both tubes determined by the blocking simultaneously neutralize each other, so that no voltage variation occurs in the grid circuit of the last audio tube Vs.

Instead of supplying the low frequency oscillations only to the tube V1 as has been stated above,

it is also possible to make these oscillations control the tubes V1 and V2 in push-pull arrangement. Preferably, the time constant determined by the condenser C1 and the resistance Rg1 is given a large value, for instance 0.1 second, in order that the charge of the condenser C1 shall not materially vary during the disturbance, Both of the arrangements referred to have the drawback that the receiver is made inoperative only when the disturbance exceeds the incoming carrier wave amplitude by a certain amount. If the latter has been modulated to for instance, the bias Egz or E of the rectifying tubes G in Figs. 1 or 2 should be given about such a value that with double the amplitude of the high or intermediate frequency oscillations induced in the coil W there just flows no current in the rectifier, provided this amplitude be kept constant by automatic volume control in the receiver. Thus, it will be appreciated that for disturbances having an amplitude smaller than double the amplitude of lthe carrier Wave, the above disturbance elimination arrangement is not started, so that these disturbances are reproduced.

The threshold sensitiveness of the disturbance elimination can be decreased by providing that the rectifier G in Fig. 1 or 2 is controlled by a separate amplifying arrangement instead of being controlled by the high or intermediate frequency Iamplifier of the receiver. This is shown in Fig. 4. Preferably, this amplifier is tuned to a wave length which lies beyond the range of wave lengths to be received, and which wave length is not engaged by a transmitting station. If, for instance, the receiving range extends from 200 to 600 meters, then the amplifier controlling the rectifier G may be tuned to a wave length between 700 and 900 meters. In this case said amplifier is affected only by disturbances, so that the threshold sensitiveness of the disturbance elimination can be appreciably reduced and the low frequency amplifier of the receiver is made inoperative even with disturbances of almost any optionally small amplitude.

casted sounds can be The third form of construction of the arrangement according to the invention is represented. in Fig. 3, and comprises a transformer which may be used in the input circuit or output circuit of the low frequency amplifier or as a coupling transformer between two or more amplifying stages. This transformer has three windings. The winding denoted by l-l is the primary winding to which the low frequency alternating voltages are supplied, for instance, by connecting it to the detector of the receiving set. In this case the secondary winding consisting of two equal winding halves lies in the grid circuit of a low frequency amplifying tube. The third winding 3 3 serves as a magnetization winding, and is fed with the direct current which in the cccurrence of a disturbance ows in a rectifier, for instance, the rectifier G shown in Fig. l or 2.

When there are no disturbances the alternating voltage applied to the primary winding is transmitted with a suitable ratio of transformation,

so that the low frequency ampiifier works in a normal manner. Upon the arrival of a disturbance the winding 3-3 gives the iron core of the transformer such a high premagnetization, that it is magnetically saturated, so that the ratio of transformation between the windings l-i and 2-2 is highly decreased. Since the magnetization flux brought about by the winding 3 3 induces opposite electromotive forces on both winding halves of the secondary winding 2-2, it will be appreciated that when the magnetizaticn current traversing the winding 3! abruptly stops, no voltage acting as a disturbance on the succeeding arrangement can occur between the terminals 2-2.

If in the above circuit arrangements the switching device, which upon receiving a disturbance causes blocking of the low frequency amplifier, has an undue inertia so that the disturbance has already entirely or partly traversed the receiving set, the time of circulation of the disturbance through the receiver can be increased with the aid of means known per se. In all cases it is advisable to make the inertia of the switching device itself as small as possible'. The circuit arrangements according to the invention involve particularly surprising eects when rapidly succeeding disturbances are to be suppressed. Such disturbances are particularly troublesome, since a disturbance of sufficient intensity deafens the ear for a certain time, so that when the individual disturbances occur in a suiiicienti-y quick succession the broadcastcd sounds reproduced by the receiver are not perceived even during the disturbance-free time intervals between said disturbances.

Since by using the arrangements according to the invention disturbances, which might cause deafening of the ear, are suppressed the broadperceived in the intermediate disturbance-free time intervals even with a rapid succession of the individual disturbances.

What is claimed is:

1. In a modulated signal carrier receiver of the type including a demodulator having a signal input circuit, a network coupled to the demodulator output circuit and arranged to transmit therethrough the modulation component of the demodulated carrier energy, a rectifier having a high frequency input circuit, means responsive to current flow of said rectifier for greatly reducing the transmission efficiency through at least a portion of the receiver between the demodulator and the output of said network whereby the viciency of a portion of the receiver transmission through said network is impaired, means responsive to signal carrier amplitude increase for decreasing the signal transmission efpreceding said demodulator to maintain the carrier amplitude at the demodulator input circuit substantially uniform, means biasing said rectifier to prevent said current flow in the absence of a high frequency voltage in the rectifier input circuit whose amplitude is greater than a predetermined amplitude of the signal carrier voltage and auxiliary means responsive to the rectifier current flow for minimizing the effect of electrical impulses produced in the receiver output by operation of said rectifier responsive means.

2. In a modulated signal carrier receiver of the type including a demodulator having a signal input circuit, a network coupled to the demodulator output circuit and arranged to transmit therethrough the modulation component of the demodulated carrier energy, a rectifier having a high frequency input circuit, means responsive to current flow of said rectifier for greatly reducing the transmission efliciency through at least a portion of the receiver between the demodulator and the output of said network whereby the transmission through said network is impaired, means responsive to signal carrier amplitude increase for decreasing the signal transmission efciency of a portion of the receiver preceding said demodulator t0 maintain the carrier amplitude at the demodulator input circuit substantially uniform, means biasing said rectifier to prevent said current flow in the absence of a high frequency voltage in the rectifier input circuit whose amplitude is greater than a. predetermined amplitude of the signal carrier voltage, said rectifier input circuit being coupled to the demodulator input circuit, and said biasing means having a magnitude such that said rectifier current flow commences only when the high frequency voltage amplitude in the rectifier input circuit exceeds double the said predetermined carrier voltage amplitude and auxiliary means responsive to the rectifier current now for minimizing the eifeet of electrical impulses produced in the receiver output by operation of said rectifier responsive means. "iflft 3. In a modulated signal carrier receiver of the type including a demodulator having a signal input circuit, a network coupled to the demodulator output circuit and arranged to transmit'there through the modulation component of the demodulated carrier energy, a rectifier having a high frequency input circuit which is tuned to a frequency outside the receiver frequency range, means responsive to current flow of said rectifier for greatly reducing the transmission eiciency through at least a portion of the receiver between the demodulator and the output of said network whereby the transmission through said network is impaired, means responsive to signal carrier amplitude increase for decreasing the signal transmission efficiency of a portion of the receiver preceding said demodulator to maintain the carrier amplitude at the demodulator input circuit substantially uniform, means biasing said rectier to prevent said current flow in the absence of a high frequency voltage in the rectifier input circuit whose amplitude is greater than a predetermined amplitude of the signal carrier voltage, and auxiliary means responsive to the rectifier current flow for minimizing the effect of electrical impulses produced in the receiver outp'ut by operation ofi said rectier responsive means.

4. In a' modulated'signal. carrier receiver of the throughrsaid network is impaired, means responsive to signal carrier amplitude increase for decreasing the signal transmission eiiiciency of a portion. of thexrecever preceding said demodulator toV maintain the carrier amplitude at the demodulator input circuit substantially uniform, means biasing said rectifier toY prevent said currentflow in the absence of Va high frequency voltage in the rectifier input circuit whose amplitude is greater than a predetermined" amplitude of the signal carrier voltage, said rectifier input circuit being coupled to the demodulatorV input circuit,

said modulation transmission'network including at least one'ampliiier tube having its input electrodes coupled to the demodulator output circuit, and said first means including a path for applying to .said input electrodes a cut-off bias derived from saidrectiiier current and additional means responsive to the rectiiier current flow for neutralizing the effect of electrical 'impulses producedV in the receiver output by said rectifier responsive means.

, 5. In a radio receiver of the type including a detector 'having an input circuit tuned to a desired signal carrier frequency, an audio amplifier having its input electrodes coupled to the detector output circuit, and automatic volume control means for'maintaining the carrier voltage amplitude at the detector input circuit at a substantially constant value, an arrangement for preventing the reproduction of electrical noise impulses impressed on the receiver, said arrangement comprising a rectifier having an input circuit coupled tosaid detector input 'circuit whereby noise voltage in the latter is` impressed on the rectifier, means biasing the rectifier to prevent current low'therethrough in the absence of a lnoise' voltage exceeding the said carrier voltage in magnitude, and means responsive to said current flow for substantially preventing transmission between the detector and audiov amplifier and means for minimizing the effect ofV electrical impulses produced in thereceiver operation of the last named means.

6'. In a radio receiver of the type including a detector having an input circuit tuned to a desired signal carrier frequency,

output by 1 an audio amplifier` having its input electrodes coupled to the detector output circuit, and automatic -volume control l `means for maintaining the carrier voltage amplitude at the` detector input circuit at a substantially constant value, an arrangement for preventing the reproduction ofV electrical noise impulses impressed on the receiver, said arrangement comprising a rectifier having an input cir-` cuit c'oupled to said detector input circuit whereby noise voltage in the latter is impressed on the. rectifier, means biasing the rectifier to prevent current flow therethrough in the absence of al noise voltage exceeding the said carrier voltage lin magnitude, means responsive to said current flow for substantially preventing transmission between the detector and audio amplifier, and

auxiliary means responsive to said current flow for neutralizing electrical impulses produced in the amplifier output circuit by operation of'said last means.

7. In a device for suppressing static in radio receivers, the combination of an antenna, a radio receiver connected to said antenna, said radio receiver having means for tuning circuits thereof to receive radio signals and static impulses occurring with said radio signals, said radio receiver alsoV including a vacuum tube having a control grid electrode and a cathode, means for negatively biasing said control grid electrode with respect to said cathode comprising an auxiliary receiver comprising a resonant circuit coupled to the Vantenna and tuned to a frequency channel not occupied by a radio signal whereby it receives only static impulses corresponding to static impulses received by said radio receiver occurring with said radio signals, said auxiliary receiver being adapted to impress the voltage of said static impulses on'said control grid of a vacuum tube of said first mentioned radio receiver as a negative grid biasing voltage so that the effect will be such as to eliminate substantially completely from the output of said radio receiver the portion of the signal and static impulses that` are coincident, means for rectifying the static impulses in said auxiliary receiver and means for impressing said rectied static impulses as a negative bias potential on said control grid of the vacuum tube in said radio receiver to bias said control grid with respectr to the cathode of the vacuum tube, in accordance with the negative potential derived from said static impulses suliciently to silence the radio receiver during the intervals of occurrence of the static impulses.

8. In a device for suppressing static in radio receivers, the combination of an antenna, a radio receiver connected to said'antenna, said radio receiver having means Vfor tuning circuits thereof to receive radio signals and static impulses occurring with said radio signals, said radio receiver also including a vacuum tube having a controlrgrid electrode and a cathode, means Yfor 'negatively biasing said control grid electrode with respect to said cathode comprising an auxiliary receiver comprising a resonant circuit coupled to the antenna land tuned to a frequency channel not occupied by a radio signal `whereby it receives only static impulses corresponding to static impulses received by said radio receiver occurring with said radio signals, said auxiliary receiver also comprising means tc amplify the voltage of said static impulses to a value such that when impressed on said control'grid of a vacuum tube of said first mentioned radio receiver as a negative grid biasing voltage the effect will be such as to eliminate substantiallyY completely from the output of said radio receiver the portion of the signal and static impulses that are coincident, means for rectifying the amplified static impulses in said auxiliary receiver, and means for impressing said ampliiied and rectiiied static impulses as a negative bias potential on said control grid of the vacuum tube in said radio receiver to bias said control grid with respect to the cathode of the vacuum tube, in accordance with the negative potential derived from said static impulses suiciently to silence the radio receiver during the intervals of occurrence of the static impulses;

receivers, the combination ceiver having means for tuning circuits thereof to receive radio signals and static impulses occurring with said radio signals, said radio receiver also including a vacuum tube having a control grid electrode and a cathode, means for negatively biasing said control grid electrode with respect to said cathode comprising an auxiliary receiver comprising a resonant circuit coupled to the antenna and tuned to a frequency channel not occupied by a radio signal whereby it receives only static impulses correspondingto static impulses received by said radio receiver occurring with said radio signals, said auxiliary receiver also comprising means to amplify the voltage of said static impulses to a value such that when impressed on said control grid of a vacuum tube of said first mentioned radio receiver as a negative grid biasing voltage the effect will be such as to eliminate substantially completely from the output of said radio receiver the portion of the signal and static impulses that are coincident. means for rectifying the amplied static impulses in said auxiliary receiver, means filtering said amplified and rectified impulses,- and means for .impressing said amplified. rectified and filtered static impulses as a negative bias potential on said control grid of the vacuum tube in said radio receiver to bias said control grid with respect to the ca hode of the vacuum tube, in accordance with the negative potential derived from said static impulses sufficiently to silence the radio receiver during the intervals of occurrence of the static impulses.

1.0. In a device for suppressing static in radio receivers. the combination of an antenna, a radio receiver connected to said antenna, said radio receiver having means ,for tuning circuits thereof to receive radio signals and static impulses occurring with said radio signals, said radio receiver also including a vacuum tube having a control grid electrode and a cathode, means for negatively biasing said control grid electrode with respect to said cathode comprising an auxiliary receiver comprising a resonant circuit tuned to a frequency channel not occupied by a radio signal whereby it receives only static impulses corresponding to static impulses received by said radio receiver occurring with said radio signals, said auxiliary receiver being adapted to impress the voltage of said static impulses on said control grid of a vacuum tube of said rst mentioned radio receiver as a negative grid biasing voltage so that the effect will be such as to eliminate substantially completely from the output of said radio receiver the portion of the signal and static impulses that are coincident, means for rectifying the static impulses in said auxiliary receiver and means for impressing said rectified static impulses as a negative bias potential on said control grid of the vacuum tube in said radio receiver to bias said control grid With respect to the cathode of the vacuum tube, in accordance with the negative potential derived from said static impulses sufficiently to silence the radio receiver during the intervals of occurrence of the static impulses.

11. In a device for suppnssing static in radio of an antenna, a radio receiver connected to said antenna, said radio receiver having means for tuning circuits thereof to receive radio signals and static impulses occurring with said radio signals, said radio receiver also including a vacuum tube having a control grid electrode and a cathode, means for negatively biasing said control grid clectrode with respect to said cathode comprising an auxiliary receiver comprising a resonant circuit tuned to a frequency channel not occupied by a radio signal whereby it receives only static impulses corresponding to static impulses received by said radio receiver occurring with said radio signals, said auxiliary receiver also comprising means to amplify the voltage of said static impulses to a value such that When impressed on said control grid of a vacuum tube of saidfirst mentioned radio receiver as a negative grid biasing voltage the effect will be such as to eliminate substantially completely from the output of said radio receiver the portion of the signal and static impulses that are coincident, means for rectifying the amplified static impulses in said auxiliary receiver, and means for impressing said ampliiied and rectiiied static impulses as a negative bias potential on said control grid if the vacuum tube in said radio receiver to bias said control grid with respect to the cathode of the vacuum tube,

in accordance With the negative potential derived from said static impulses sulciently to silence the radio receiver during the intervals of occurf rence of the static impulses.

12. In a device for suppressing static in radio receiversthe combination of an antenna, a radio receiver connected to said antenna, said radio receiver having means for tuning circuits thereof to receive radio signals and static impulses occurring v/ith said radio signals, said radio receiver also including a vacuum tube having a control grid electrode and a cathode, means for negatively biasing said control g1id electrode with respect to said cathode comprising an auxiliary receiver comprising a resonant circuit tuned to a frequency channel not occupied by a radio signal whereby it receives only static impulses corresponding to static impulses received by said radio receiver occurring with said radio signals, said auxiliary receiver also comprising means to amplify the voltage of said static impulses to |a value such that when impressed on said control grid of a vacuum tube of said iirst mentioned radio receiver as a negative grid biasing voltage the eifect will be such as to eliminate substantially completely from the output of said radio receiver the portion of the signal and static iinpulses that are coincident, means rectifying the amplified static impurses in said auxiliary receiver, means ltering said amplified and rectified impulses, and means for impressing said amplified, rectified land iiltcred static impulses as a negative bias potential on said control grid of the vacuum tube in said radio receiver to bias said control grid with respect to the cathode of the vacuum tube, in accordance with the negative potential derived from said static impulses sufcie-ntly to silence the radio receiver during the intervals of occurrence of the static impulses.

i3. In a modulated carrier wave receiver system of the type including a carrier ivave arnpliiier, a detector and a modulation current amplier, an arrangement for automatically controlling the receiver operation when undesired electrical impulses having a period of the order of '1&5 second are impressed on the receiver, said arrangement comprising an alternating current rectifier having a threshold sensitivity such that solely electrical impulses having an amplitude substantially double the carrier wave amplitude at the carrier amplifier output are rectified, said rectifier having an input circuit which is tuned to a frequency adjacent that of the receiver system, and means responsive to the rectified output of the rectifier for rendering inefficient the modulation current transmission between solely the detector and modulation amplier.

14. In a modulated carrier wave receiver system of the type including a carrier wave amplier, a detector ,and a modulation current amplier, an arrangement for automatically controlling the receiver operation when undesired electrical impulseshaving a period of the order of 1&5 second are impressed on the receiver, said arrangement comprising an alternating current rectier having-a threshold sensitivity such that solely electrical impulses having an amplitude substantially double the carrier wave amplitude at the carrier amplifier output are rectified, said rectier having an input circuit tuned to a frequency different from that of the receiver system, means responsive to the rectilied output of the rectifier for rendering ineilicient the modulation current transmission between solely the detector and modulation amplifier, said responsive means .being constructed and arranged to prevent the production of a disturbing potential pulsation at said modulation current amplifier.

15. In a modulated carrier wave receiver system of the type including a carrier wave amplier, a detector and a modulation current amplier, an arrangement for automatically controlling the receiver operation when undesired electrical impulses having a period of the order of 1/5 second are impressed on the receiver, said arrangement comprising an alternating current rectier having a threshold sensitivity such that solely electrical impulses having an amplitude substantially double the carrier wave amplitude at the carrier ampliiierA output are rectied, means responsive to the rectied output of the rectifier for rendering'ineiilcient the modulation current transmission between the detector and modulation amplifier, said rectifier having an input circuit tuned to a frequency adjacent that to which the said receiver is tuned.

16. In a device for suppressing static in radio receivers, the combination of an antenna, a radio receiver connected to said antenna, said radio receiver having means for tuning circuits thereof to receive radio signals and static impulses occurring with said radio signals, said radio receiver also including a vacuum tube having a control grid electrode and a cathode, means for negatively biasing said control grid electrode with respect to said cathode comprising an auxiliary receiver comprising a resonant circuit coupled to the antenna and a controllable network whereby the output of said auxiliary receiver comprises only' static impulses corresponding to static impulses received by said radio receiver occurring with said radio signals, said auxiliary receiver being adaptedV to impress the voltage of said static impulses on said control grid of a vacuum tube of said rst mentioned radio receiver as a negative grid biasing voltage so that the eifect will be such as to eliminate substantially completely from the output of said radio receiver the portion of the signal and static impulses that are coincident, means for rectifying the static impulses in said'auxiliary receiver and means for impressing said rectied static impulses as a negative bias potential on said control grid of the vacuum tube in said radio receiver to bias said control grid with respect to the cathode of the vacuum tube, in accordance with the negative potential derived from said static impulses sufliciently to silence the radio receiver during the intervals of occurrence of the static impulses.

e 17. In a device ier suppressing static in radii receivers, the combination of an antenna, a radio receiver connected to said antenna, said radio receiver having means for tuning circuits thereof to receive radio signals and static impulses occurring with said radio signals, said radio receiver also including a vacuum tube having a control grid electrode and a cathode, means for negatively biasing said control grid electrode with respect to said cathode comprising an auxiliary receiver comprising a resonant circuit coupled to the antenna and a controllable network whereby the output of said auxiliary receiver comprises only static impulses corresponding to static impulses received by said radio receiver occurring with said radio signals, said auxiliary receiver also comprising means to amplify the voltage of said static impulses to a value such that when impressed on said control grid of avacuum tube of said first mentioned radio receiver as a negative grid biasing voltage the eiect will be such as to eliminate substantially completely from the output of said radio receiver the portion of the signal and static impulses that are coincident, means for rectifying the ampliiied static impulses in said auxiliary receiver, and means for impressing said amplied and rectied static impulses as a negative bias potential on said control grid of the vacuum tube in said radio receiver to bias saidcontrol grid with respact to the cathode of the vacuum tube, in accordance with the negative potential derived from said static impulses sufliciently to silence the radio receiver during the intervals of occurrence of the static impulses.

l8r. In a device for suppressing static in radio receivers, the combination of an antenna, a radio receiver connected to said antenna, said radio receiver having means for tuning circuits thereof to receive radio signals and static impulses occurring with said radio signals, said radio receiver also including a vacuum tube having a control grid electrode and a cathode, means for negatively biasing said control grid electrode with respect to said cathode comprising an auxiliary receiver comprising a resonant circuit coupled to the antenna and a controllable network whereby the output of said auxiliary receiver comprises only static impulses corresponding to static impulses received by said radio receiver occurring with said radio signals, said auxiliary receiver also comprising means to amplify the voltage of said static impulses to a value such that when impressed on said control grid oa vacuum tube of said rst mentioned radio receiver as a negative grid biasing voltage the effect will be such as to eliminate substantially completely from the output of said radio receiverY the portion of the signal and static impulses that are coincident, means for rectifying the amplified static impulses in said auxiliary receiver, means filtering sa'id amplified and rectified impulses,and means for impressing said ampliedrectied and filtered static impulses as a negative bias potential on said control grid of the vacuum tubein said radio receiver to bias said control grid with respect to the cathode of the vacuum tube, in accordance with the negative potential derived from said static impulses suiiciently to silence the radio receiver during the intervals of occurrence of the static impulses.

BERNARDUS D. H. 'I'ELLEGEN. VIVIAN COHEN HENRIQUEZ. 

